The present invention relates to a system and method for heating fresh water on boats and other marine vessels. More specifically, the present invention relates to improved heating systems employing heat exchangers that function to transfer heat energy to fresh water while a boat or marine vessel engine is running at low rpms.
Boats and other marine vessels use a number of energy sources to heat fresh water stored in a hot water tank. The source chosen at a particular time generally depends on whether the boat is away from dock and how the boat is being operated. When the boat is at a dock with an electrical power supply available, the hot water tank may be heated by supplying an electrical current through a resistance heating element immersed in the tank. When the boat is away from dock, however, the boat engine is often used as the source of heat. The hot water tank is typically heated by running the engine and cycling engine coolant through a closed loop that passes through the hot water tank to transfer heat to the fresh water.
Conventional closed loop water heating systems are often relatively inefficient, however, for heating fresh water on boats. This is most apparent when the boat engine is idling at relatively low rpms and subject to low loads. During high rpms or high engine loads, there is little difficulty in heating the hot water tank due to the enormous amount of heat generated in the engine. During low load operation and low rpms, however, a relatively low amount of heat is produced by the engine. In addition, the coolant pipe passing through the hot water tank provides a relatively small surface area in contact with the water, resulting in relatively low heat transfer. Corrosion and scaling on the conduit can diminish heat transfer even further. As a result, boat captains are frequently compelled to run the engine at high rpms for significant periods of time to supply enough hot water for multiple showers. Running a boat engine for an extended period of time results in unnecessary fuel consumption and causes unnecessary strain on the boat""s engine.
With the foregoing in mind, the present invention provides an improved water heating system for use on boats, marine vessels and the like. The heating system includes a hot water tank connected with a heat exchanger such as a supplemental external heat exchanger. The heat exchanger, which may be a plate heat exchanger, has first and second flow paths. The first flow path is connected with the hot water tank in a closed loop to cycle water between the hot water tank and the heat exchanger. The second flow path is connected to an engine coolant pipe which may also pass from the boat engine through the hot water tank. A circulation pump is connected between the hot water tank and the first flow path in the heat exchanger to control the cycling of water between the tank and the heat exchanger. Since heated water is circulated through the system, the system provides more efficient heat transfer than prior art systems that use convection heat transfer in static hot water tanks.
Coolant fluid in the coolant line for the engine is cycled through both the hot water tank and the heat exchanger as the engine operates. In one embodiment, operation of the circulation pump is controlled by a manual switch. In another embodiment, the circulation pump is controlled automatically by operating conditions in the boat. In particular, the circulation pump may be controlled by a temperature sensor in the hot water tank. When the temperature drops to a minimum temperature, the sensor sends a signal to activate the circulation pump. Water is then cycled between the hot water tank and the first flow path in the heat exchanger until the temperature sensor detects a maximum temperature in the hot water tank. The circulation pump is then switched off. The circulation pump may also be controlled by other conditions in the boat, such as engine rpms.
In accordance with the invention, a supplemental water heating kit may be used to supplement or retrofit an existing hot water tank of a boat through cooperation with the coolant line for the engine of the boat. The existing hot water tank may include a cold water inlet for enabling water to be input to the hot water tank and a hot water outlet to enable hot water stored in the tank to be drawn from the water tank. An engine coolant conduit connected with the coolant line from the boat engine may run through the hot water tank to heat water in the hot water tank. In such an embodiment, the supplemental water heating kit may include a heat exchanger adapted to be positioned externally of the hot water tank. The heat exchanger may include an exchanger water inlet and an exchanger water outlet with a first flow path extending through the heat exchanger from the exchanger water inlet to the exchanger water outlet. The hot water tank may be fluidly connected to the first flow path using a variety of piping configurations. The first flow path may be fluidly connected with the cold water inlet and the hot water outlet of the hot water tank. Alternatively, the first flow path may be fluidly connected to circulation inlet and circulation outlet ports on the hot water tank that are distinct from the cold water inlet and hot water outlet on the hot water tank. The heat exchanger may include a coolant inlet and a coolant outlet with a second flow path extending through the heat exchanger from the coolant inlet to the coolant outlet. The second flow path is provided for fluid connection with the coolant line from the engine of the boat so that heated engine coolant may be circulated through the second flow path of the heat exchanger.
A water pump may also be provided in the kit for connection in fluid communication between the hot water tank and the exchanger water inlet of the heat exchanger. The pump operates to circulate water from the hot water tank through the first flow path of the heat exchanger as heated engine coolant from the engine is circulated through the second flow path of the heat exchanger to effect heat transfer from the heated engine coolant to the water circulating through the first flow path. The water heated along the first flow path of the heat exchanger is then reintroduced back into the hot water tank.
The kit may also include a water outlet line for the heat exchanger for fluid connection between the exchanger water outlet and the hot water tank to enable heated water from the heat exchanger to be circulated from the first flow path back into the hot water tank. In a specific arrangement, the water outlet line may be connected between the exchanger water outlet and the cold water inlet of the hot water tank. The water outlet line may alternatively be connected between the exchanger water outlet and a circulation inlet port on the hot water tank that is distinct from the cold water inlet.
The kit may also include a water inlet line for the heat exchanger for connection between the hot water outlet of the water tank and the exchanger water inlet of the heat exchanger. In specific operation, the water pump may be connected between the hot water outlet of the hot water tank and the exchanger water inlet by connection into the water inlet line.
The kit may also comprise a coolant inlet line for fluid connection between the coolant line of the engine and the coolant inlet of the heat exchanger. A coolant outlet line may also be included in the kit for fluid connection between the coolant outlet of the heat exchanger and the coolant line of the engine so that heated engine coolant may be circulated from the coolant line of the engine through the second flow path.
A one-way valve may be provided in the kit for connection with the cold water inlet of the hot water tank, for example, along a cold water source line that supplies cold water to the cold water inlet of the hot water tank. The water outlet line from the heat exchanger can be connected with the cold water source line intermediate the hot water tank and the one-way valve so that the one-way valve prevents back flow of heated water from the heat exchanger and the hot water tank toward the cold water source. A second one-way valve may be provided for connection with the hot water outlet of the hot water tank, for example, along a hot water supply line from the hot water tank. The water inlet line to the heat exchanger can be connected with the hot water supply line intermediate the one-way valve and the hot water tank so that the one-way valve prevents back flow of water toward the hot water tank as the pump operates to circulate water from the hot water tank to the heat exchanger.
A thermal mixing valve may also be provided with the kit to prevent heated water from being discharged from the system at scalding temperatures. The thermal mixing valve may be installed in the hot water supply line that leaves the hot water tank. The mixing valve is connected to a source of cold water and periodically draws a volume of cold water into the hot water supply line to maintain the water temperature below a maximum temperature as the water leaves the system. The thermal mixing valve may be connected to a thermostat control that allows individuals to select a maximum temperature for hot water output.